Interesting this produces a truthy or falsy string

<?php
wp_localize_script( 'pwcc-functions', 'pwccConfig', array(
  'isSingle' => is_single(),
) );

but this is all lovely and boolean.

<?php
wp_localize_script( 'pwcc-functions', 'pwccConfig', array(
  'is' => array(
    'single' => is_single(),
  )
) );

It’s an abuse of the localisation function so I can see why it expects a string.

Coincidently, a related trac ticket was opened a few hours after this post.